This invention relates to a signal synthesizer in which a wide frequency range signal is synthesized from a narrow frequency range signal.
There are many signal transmission systems in which a wide frequency range signal transmission is hard to obtain. Typical examples are an AM radio broadcasting system, analog tape recorder with slow tape running speed, telephone network, etc. When a superheterodyne AM receiver is considered, even if AM broadcasting stations transmit a wide frequency range musical source, the sound quality of music reproduced from the AM receiver is very poor because the reproduced sound lacks overtone or higher harmonic frequency components. A conventional high-frequency enhancing tone controller (or equalizer) may somewhat improve the sound quality, but frequency compensation by means of such a tone controller inevitably invites increase of noise. Further, although a tone controller or tone equalizer can compensate the level down of signal components, it cannot compensate nonexistent or excessively level-downed signal components.